Make your own Thermometer!

A thermometer is a device used to measure the temperature. Now that it's between summer and fall, the temperatures will be changing a lot. Use your homemade thermometer to see whether it's hot, or cold!

Take the lid off your bottle, and fill it with water. Put a few drops of food coloring in the water so you can see it better. Make sure you don't spill any or it might stain something!

Make a hole in the centre of the bottle cap. Ask an adult to help you with it. Screw the bottle cap back on the bottle.

Melt the wax, or smush the plasticine around the straw, and the edge of the cap. If you are using wax, make sure you get help from a parent so you don't burn yourself!

Place a white card behind the straw so that its water level can be seen easily.

Try putting your bottle in warm places, and cool places. Watch the water levels when you hold it by the freezer, or in the sun.

What happened?

If your thermometer works properly, the water in the straw gets higher when it's hotter, and lower when it's cooler. Why does it do that? Everything is made of molecules. Molecules are kind of like building blocks, or lego. But there are always small spaces between the molecules. When something is hot, the space in between the molecules gets bigger, and the molecules spread out. When something is cold, the space in between the molecules gets smaller, and the molecules get closer together. That's why the water in your thermometer goes up when it's hot, and down when it's cold. The water expands when it experiences warmer temperatures, and the water contracts when it experiences cooler temperatures.

More?

What? You want to know the exact temperature with your thermometer? Try this. Place a commercial thermometer next to your homemade one. Draw a line on the white card next to the water level in the straw. On this line, write the temperature you read on the commercial thermometer. Take the two thermomters to colder and warmer places, and record the commercial thermometer readings next to the water levels on your homemade scale. The more temperatures you record, the more exact your thermometer will be.

Adapted from The How and Why Wonder Book of Beginning Science by Dr. Jerome J. Notkin, 1985.